Seizure 1992; 1: 145- 147

CLINICAL CONTROVERSY: CONVERSATION WITH CLINICIANS*

Who needs neurological The diagnosis of epilepsy can be difficult involves four separate steps.

imaging? but

from other (1) Seizures must be differentiated forms of episodic disorder. (2) Seizures must be classified and, in particular, acute symptomatic seizures must be differentiated from those occurring as part of an epilepsy. (3) The diagnosis of an epilepsy syndrome should be made where appropriate. (4) Any underlying aetiology should be identified. As part of this last step it is often recommended that computed tomography (CT) or magnetic resonance imaging (MRI) should be undertaken in all patients presenting with seizures or epilepsy. This approach is advocated for a number of reasons, most of which relate to the possibility that any patient presenting with epilepsy for the first time may be harbouring a cerebral tumour. Advocates of this policy may advance some or all of the following arguments. (1) The patient has an absolute right to be reassured that they do not have a cerebral tumour, irrespective of the degree of risk of such a lesion being present. (2) If I don’t diagnose a tumour that is present: (a) I will look foolish, (b) I may be sued. This author believes that an unselective approach to neurological imaging at the time of diagnosis of epilepsy or seizures is irresponsible in a health care system that provides less than unlimited resources for the care of patients. It will result in resources being diverted away from their most efficient use for the population of people with epilepsy. I would This section of the journal will contain a personal account of a particular clinician’s practice related to some controversial area of epilepsy management. The clinician can remain anonymous if he/she wishes to. The Correspondence Columns are open for comment on this contribution to our Clinical Controversy section. The Editor l

1059-1311/92/030145+03

$03.00/O

support this contention lines of argument.

with

the

following

FALSE NEGATIVES AND FALSE POSITIVES IN IMAGING

CT scanning at presentation of epilepsy has certainly, in the past, been associated with false negative scans’. That is, patients subsequently were diagnosed as having tumours who had an initial CT scan reported as being normal. It may be argued that the improved technology of modern generation CT and also MRI reduces this possibility, but it cannot be completely excluded. It must also be noted that as CT and MRI become more widely distributed, investigation may be reported by and acted upon by less expert radiologists and clinicians. Subtle lesions may therefore be missed. MRI, in particular, is an investigation with enormous sensitivity and little specificity. There may be a very real danger that this technology may identify coincidental lesions that may be misdiagnosed (false-positive) as tumours and inappropriate treatment, on occasion, offered. All neurologists must have seen cases where this has occurred.

UNSELECTIVE IMAGING IGNORES THE CLINICAL CLASSIFICATIONS OF SEIZURES AND EPILEPSIES

During the last 10 years, generally agreed classifications of seizures2 and epilepsy syndromes3 have been proposed. One implication of these classifications is the identification of age-specific syndromes of idiopathic generalized epilepsy. It must be remembered that the incidence of epilepsy is greatest in infants and children, a group in which supratentorial tumours are extremely rare. Age is an important factor that should be considered during investigations. Approximately one third to one half of @ 1992 Bailliere Tindall

146

patients presenting with seizures after the age of 5 years will have an idiopathic generalized epilepsy syndrome. These age-related syndromes, which include childhood absence, juvenile absence, juvenile myoclonic epilepsy and wakening tonic-clonic seizures are all associated with generalized spike wave and have no association with cerebral tumours. Where a positive clinical diagnosis of one of these epilepsy syndromes can be made, it does not seem justified to subject patients to imaging investigations.

IS IT POSSIBLE TO IDENTIFY GROUPS OF PATIENTS AT HIGH RISK OF CEREBRAL TUMOUR? The relationship between intracranial tumour and epilepsy is well recognized by doctors and by the public. About 40% of patients with tumours have seizures as their first symptom4. Very often the interval between the first seizure and the diagnosis of the tumour and any development of other complicating neurological problems is prolonged596. This reflects the fact that the majority of tumours that present with epilepsy tend to be benign. Thus, oligodendrogliomas are complicated by epilepsy in 80-90% of cases, meningiomas in 40-60% of cases, and astrocytomas in 60-70% of cases. Only 30-40% of patients with malignant gliomas or glioblastoma multiforme have seizures7. Brain tumours are responsible for lateonset epilepsy in only about 10% of cases from many series. The incidence of tumours rises steeply where seizures are clearly focal in onset’,‘. Simple partial seizures with symptoms suggesting onset in the frontal, parietal and occipital lobes seem to carry the highest risk of being associated with tumours4’10. The incidence of tumours as a cause for complex partial seizures is lower (about 15%)11. Overall, Gastaut (1976)12, from a specialist centre, found that 16% of 76 patients with epilepsy beginning over the age of 20 years had tumours on CT scanning. These early studies can, of course, be criticized as showing a falsely low frequency of tumour epilepsies, having been undertaken in the era before modern neurological imaging. In less selected populations of patients the incidence of tumours found on CT scanning is, however, even lower. They were found in 6% of patients registered with the National General Practitioner Survey of Epilepsy13 and only 3%

Clinical controversy

of adult patients investigated following a first seizure14. However, the combination of clearly focal seizures, focal slowing on the EEG and the presence of unexplained focal neurological signs predicts the presence of a tumour on CT scanning in a high proportion of case& 15.

DOES THE EARLY IDENTIFICATION OF A CEREBRAL TUMOUR MAKE MANAGEMENT EASIER OR MORE DIFFICULT? Whilst meningiomas should clearly be treated surgically at an early stage where this is practical, technically possible, and when the patient is not old or infirm, meningiomas are likely to account for less than 10% of cerebral tumours diagnosed as causing epilepsy. There is a considerable dilemma about the management of primary intercerebral tumours that present with epilepsy. Both retrospective and prospective surveys of survival in patients with primary intracerebral tumours would indicate that the presentation with epilepsy carries a relatively favourable prognosis6,i6. Patients presenting with epilepsy are less likely to have focal neurological signs, more likely to have a non-enhancing low-density lesion on CT scan and to be significantly younger than patients whose first symptom of their tumour is not epilepsy. All these factors, in addition to the presentation with epilepsy, have a favourable effect on survival and indicate a high probability of a low grade relatively benign tumour. Clinicians are uncertain whether to embark upon early surgical treatment (biopsy for histological verification with or without tumour debulking or resection and appropriate radiotherapy), which carries some risks of morbidity and mortality, or whether to defer such tumour-related treatment until such time as the patient develops other evidence of progressive neurological problems. No prospective randomized study of conservative versus more aggressive management in patients with low grade gliomas has been performed despite identification of the need for such a study’,17*18. Whilst the evidence that postoperative radiotherapy prolongs survival in malignant gliomas is convincing, at least for those who survive their surgery in good condition1g-21, its role in low grade gliomas is disputed and certainly not established. There are considerable concerns about the possible effects of cranial irradiation in patients with the potential for long-term surviva122. Hope-

Who needs neurological

imaging?

147

fully, a prospective randomized study organized by the Medical Research Council will go some way to answering these dilemmas but, at present, the early diagnosis of an intrinsic cerebral tumour by imaging, when the patient has no other symptoms than their epilepsy, does not immediately offer patients a combination of treatment options that have proven benefit or quantifiable risk. Patients are left to make difficult decisions about their management with a minimum of information.

CONCLUSION

4.

5.

6.

7.

8.

This author believes that early unselective CT scanning at the diagnosis of epilepsy is unjustified, but does believe that neurological imaging is of vital importance to the management of the ZO-30% of patients who present with epilepsy who never achieve good seizure control and who, at an early stage, can be identified as having a medically refractory epilepsy. This group of patients, which includes those with atrophic as well as potentially neoplastic lesions need to be considered for a surgical approach to their epilepsy and it is here that relatively few health care systems provide the financial resources to meet the potential demand. I therefore firmly believe that we should direct scarce imaging resources away from patients presenting with epilepsy to that population where neurological imaging has significant therapeutic implications.

9. 10. 11.

12. 13.

14. 15.

16.

17

DAVID

CHADWICK

The Walton Centre surgery Rice Lane Liverpool L9 1AE UK

for Neurology

& Neuro-

REFERENCES 1. Young, AC., Bog Costazi, J., Mohr, P.D. and Forbes, W. Is routine computerised axial tomography in epilepsy worthwhile? Lancet 1982; ii: 1446. 2. Commission on Classification and Terminology of the International League Against Epilepsy. Proposal for revised clinical and electroencephalographic classification of epileptic seizures. Epilepsia 1981; 22: 489501. 3. Commission on Classification and Terminology of the International League Against Epilepsy. Proposal for

18.

19.

20.

21.

22.

revised classification of epilepsies and epileptic syndromes. Epilepsia 1989; 30: 389-398. Penfield, W. and Jasper, H. Epilepsy and the Functional Anatomy of the Human Bruin. Boston, Little Brown, 1954. Douglas, D.B. Interval between first seizure and diagnosis of brain tumour. Disease of the Nervous System 1971; 32: 255. Smith, D.F., Hutton, J.L. and Sandemann, D.R. et al. The prognosis of primary intracerebral tumours presenting with epilepsy: The outcome of medical and surgical management. Journal OfNeurology Neurosurgery and Psychiatry 1991; 54: 915-920. Lund, M. Epilepsy in association with intracranial tumour. Acta Psychologica Neurologica Scandinavica 1952; (suppl); 81. Raynor, R.B., Paine, R.S. and Carmichael, E. A. Epilepsy of late onset. Neurology 1959; 9: 111. Sumi, S.M. and Teasdall, R.D. Focal seizures. A review of 150 cases. Neurology 1963; 13: 582. Mauguiere, F. and Courjon, J. Somatosensory epilepsy: A review of 127 cases. Brain 1978; 101: 307. Currie, S., Heathfield, K.W.G., Henson, R.A. and Scott, D.F. Clinical course and prognosis of temporal lobe epilepsy. Bruin 1971; 94: 173. Gastaut, H. Conclusions: computerized transverse axial tomography in epilepsy. Epilepsia 1976; 17: 337. Sander, J.W.A.S., Hart, Y.M., Johnson, A.L. and Shorvon, S.D. National general practice study of epilepsy: newly diagnosed epileptic seizures in a general population. Lancet 1990; 336: 1267. Hopkins, A., Garman, A. and Clarke C. The first seizure in adult life. Lancet 1988; i: 721. Dam, A.M., Fuglsang-Frederiksen, A., Svarre-Olsen, U. and Dam, M. Late-onset epilepsy: aetiologies, types of seizure and value of clinical investigation, EEG and computerized tomography scan. Epilepsia 1985; 26: 227. Scott, G.M. and Gibberd, F.B. Epilepsy and other factors in the prognosis of gliomas. Acta Neurologicu Scandinauica 1980; 61: 227-239. Wroe, S.J., Foy, P.M., Shaw, M.D.M., Williams, I.R., Chadwick, D., West, C. and Towns, G. Differences between neurological and neurosurgical approaches in the management of malignant brain tumours. British Medical Journal 1986; 293: 1015-1018. Cairncross, J.G. and Laperriere, N.J. Low-grade glioma: to treat or not to treat? A reply. Archives of Neurology 1990; 47: 1139-1140. Anderson, A.P. Post-operative irradiation of glioblastomas. Results in a randomised series. Actu Radiologica 1978; 17: 475-484. Kristiansen, K., Hagen, S., Kollevoid, T. et al. Combined modality therapy of operated astrocytomas grades 3 and 4. Confirmation of the value of post-operative irradiation and lack potentiation of bleomycin on survival time. Cancer 1981; 47: 649-652. Walker, M.D., Green, S.B., Byar, D.P. et al. Randomised comparisons of radiotherapy and nitrosoureas for the treatment of malignant glioma after surgery. New England Journal of Medicine 1980; 303: 13231329. Imperato, J.P., Paleologos, N.A. and Vick, N.A. Effects of treatment on long-term survivors with malignant astrocytomas. Annals OfNeurology 1990; 28: 818-822.

Who needs neurological imaging?

Seizure 1992; 1: 145- 147 CLINICAL CONTROVERSY: CONVERSATION WITH CLINICIANS* Who needs neurological The diagnosis of epilepsy can be difficult invo...
336KB Sizes 0 Downloads 0 Views